EMPLOYMENT: The fuze is pressumably used as an alternative in the H.E. shell (K.Gr. 39) and the H.E.B.C. shell (K.Gr. 38 (Hb)) for the 17-cm K.Mrs. Laf. (See fig. 595A.)

DATA:

Over-all length: 4.812 inches.

Maximum diameter: 2.25 inches.

Threaded length: 0.5 inch.

Number of threads: 4 RH.

CONSTRUCTION: The fuze has a mechanical time action with a maximum time of running of 90 seconds and a graze action of the normal German type. The time mechanism ap-pears to be a 45-second mechanism modified by a change in the ratio of the gear train and an increase in the strength of the main spring. The weight of the fuze is 1 pound 12 ounces.

In external appearance the fuze consists of a flat-topped cone-shapped head of alumi-num secured to a dull steel body near its base by a bright steel securing ring. The upper part of the body is coned above the flange to match the head. Below the flange is screw-threaded for insertion in the shell and below the thread there is a plain cylindrical portion.

The designation of the fuze, "Dopp.Z. S/90/45", is stamped in the body above the flange. Rectangular key slots for setting are formed in the head and the body and a setting ar-row for percussion action is engraved in the head adjacent to the slot. When inserted in the shell the fuze protrudes to the extent of approximately 3 inches. The diameter of the screw-threaded part is 1.8 inches.

Body. The body is recessed at the base to accommodate the shutter assembly and, equally spaced around the recess, there are three vertical channels for the bolty secur-ing the time mechanism unit. An additional vertical channel, closed at the base by a screwed plug, accommodates the holder of the detonator for the time action. A radial channel in the wall of the recess contains a brass centrifugal bolt and is closed at the outer end of a screwed plug. A portion of the top of the recess is cut away to permit movement of the bolt, and a flash channel in the center of the top connects with a re-cess in the upper part of the body.

Figure 595A – Dopp.Z. S/90/45

The upper recess contains the graze pellet of the percussion mechanism and is connec-ted to the channel containing the detonator for the time action by an inclined channel which enters the recess near its base. Near the top, the recess is enlarged to form a platform on which four centrifugal segments of brass are fitted on steel pivots. Above this the recess is screw-threaded to receive the percussion striker holder. The coned flanged top of the body is recessed to form a platform for the time mechanism unit and is screw-threaded internally to receive the securing ring for the aluminum head. Two holes, diametrically opposite, are formed in the platform to receive the locking plungers of the time unit. There is also a locating stud for the unit, and a circular seating for fiber was-her. Four small screws are inserted through the coned flange to lock the securing ring when the fuze is tensioned during assembly.

Percussion Mechanism. The graze pellet, carrying an igniferous detonator secured by a perforated screwed plug, is of brass with a shoulder near the top which is engraved by the four centrifugal brass segments. The segments are retained in a position overlapping the pellet by an expanding spring ring. A spiral creep spring is fitted between the pellet and a striker holder which consists of a steel disk screwed into the top of the recess containing the graze mechanism. The striker protruding from its underside has a pyramid shaped point.

Shutter Assembly. The assembly contained in the lower recess in the body consists of a copper plate shutter moving in a guideway formed in the top of a cylindrical aluminum holder. The holder is a central flash hole and is recessed at one side of the centrifugal bolt which, under the pressure of its spiral springs, bears against the outer end of the shutter and keeps the shutter in a position tasking the flash hole in its aluminum holder. The centrifugal bolt is a cylindrical pellet of brass with recess at its outer end to locate the inner end of a spiral spring. The outer end of the spring is held under the compres-sion by the screwed plug posing the radial channel in the wall of the recess and located by a circular grove in the inner face of the plug. A thin disk of tin, with a central flash hold and with part of its circumference cut away for the centrifugal bolt, is placed on top of the shutter holder. The recess containing the shutter assembly is closed at the base by a screwed plug which has a central flash hole. The flash hole is closed by a thick disk of tin fitted between the inner face of the plug and the Base of the shutter holder.

Head Assembly. The flat-topped aluminum head is in the shape of a cone with a cylindrical portion near the base. An external flange is forrmed at the base which supports the ten-sioning wire. The underside of the flange is cutaway at four places to receive corres-ponding projections at the base of the dome. The dome, fitted inside the head, is of thin aluminum and is in the form ??an inverted cup which fits over the time-mechanism unit and is keyed to the flange at the base of the aluminum head by four projections at its base. The ??side of the top of the dome is shaped to form a race against which the hand on the top of the time unit when rotating. Part of the race is cut away so that the hand can be pushed upwards by its spring when in alinement with the slot so formed. The head of the fuze is secured to the body by a steel ring which screws into the internal screw-thread above the flange. Between the base of the securing ring and the flange at the base of the head there is a length of waved spring wire which is compressed bet-ween the ring and the flange when the ring is screwed down. By this means the tension-ing of the head is adjusted during the assembly so that is can be turned for setting but will not slip.

Time Mechanism Unit. The time mechanism is assembled in a cylindrical unit of superimpo-sed brass plate with an aluminum hand on the top and two locking plungers in slots cut down diametrically opposite sides of the cylindrical assembly. The plungers are compara-tively weighty and consist of steel strips tapering toward the base on the inner side. On the outer side of each, approximately at the center, a projecting vertical knife edge is formed. A spring-loaded ball protruding from one side of the plunger engaged a corres-ponding recess in the slots and thus supports the plungers which protrude below the base of the unit into recesses in the fuze body. The mechanism is similar to that in the S/30 and S/60 s fuzes; that is, it consists principally of a spring-loaded striker held off the detonator by an eccentric cam collar on the striker which is supported by a pillar and a ecntrifugal safety catch. The cam collar is kept in this position by a safety lever which fits over flats formed on the forward end of the striker and is held by the ring shaped center of the hand. The hand, with a sprial spring beneath it, is keyed to rotate with the center arbor under the control of a train of gear wheels and an escapement and, before firing is held by the pivoted trigger. Adjacent to the trigger a safety bridge is fitted which overlaps the hand to prevent functioning at settings of less than approximately 1 se-cond. The spring plunger supporting the trigger engages in the end of the trigger instead of the inner side as with the S/30 and S/60 s fuzes. The use of a stronger main spring, which is of wider strip than the original, has resulted in the use of a thin steel disk in-stead of the normal base of the spring barrel to support the spring.

Figure 595B – Dopp.Z. 28 K

ACTION: The time of running is governed by the size of the arc extending counterclock-wise between the position of the hand when held by the trigger and the position of the slot in the dome hand race. The fuze is set by turning the head with the aid of a setting device which consists of a graduated ring surrounding a movable ring on which there is a setting index and a handle. The device is placed over the fuze; and the outer ring, bear-ing the graduations, is clamped by a key engaging in the key slot above the flange in the fuze body. A key in the inner ring, bearing the index, engages in the key slot in the head of the fuze. The inner ring is then rotated by means of its handle unit the index is alined with the required graduation and takes with it the head of the fuze. The dome inset, with the hand race formed in its upper part, is rotated with the head to the set position. The turning of the head is retarded by the waved wire tension spring between the secur-ing ring and flange at the base of the head.

On acceleration the two tapered locking plungers set back into the recesses in the top of the body. As their wider protions with the protruding knife egdes move back through the slots, the knife edges cut into the wall of the dome and thus prevent rotation of the dome relative to the mechanism unit. At the same time, the trigger hinging on its pivot, sets back and releases the hand.

The small spring-loaded plunger in the trigger is then free to emerge and thus prevents the trigger rebounding. The release of the hand enables the main spring to rotate the center arbor, moves clear of the safety bridge and is pressed up against the hand race in the top of the dome by the spiral spring in the top of the arbor beneath the hand center.

During flight, the safety catch is swung clear of the cam collar on the striker by centri-fugal force and the striker is then supported only by the pillar. When the rotating hand reaches the slot in the hand race, it is forced upwards by its spring and thus releases the safety lever keyed to the top of the striker. The striker, with the lever, is then ro-tated by the pressure of its spring commed with the effect of the inclined surface of the collar. The striker is driven away from the safety lever by its spring and pierces the de-tonator. The flash from the detonator, directed by the shape of the detonator holder, passes into the lower part of the recess containing the graze pellet and follows the same course as that described for the percussion action.

Percussion Action. When set for percussion the arrow on the head of the fuze coincides with the index line on the securing ring, and the key slots in the head and body are in alinement. At this setting, the slot in the hand race of the dome is masked by the safety bridge so that although the hand released when acceleration occurs, it cannot rise through the slot ot release the safety lever and the striker.

During flight, the coil of the expanding spring ring, surrounding the segments engaging the shoulder of the graze pellet, is enlarged and the segments are swung clear of the pellet by centrifugal force. At the same time, the contrifugal bolt is thrown outwards, compressing its spring, and the shutter opens.

On graze, the graze pellet overcomes the creep spring by its momentum and carries the detonator forward to be pierced by the striker. The flash from the detonator passes through the hole in the base of the recess, through the channel exposed by the open shutter, perforates the tin disk and emerges through the hole in the screwed plug at the base of the fuze.

REMARKS: The Dopp.Z. 28 K is identical to the Dopp.Z. S/90/45 except for variations in the gear train ratios used in the clockwork mechanism (See fig. 595B).

The Dopp.Z. 28 K is employed in the 21-cm K.Gr. 38 and 28-cm Gr. 39 projectiles.